Brighton moved into seventh in the Championship after a 1-0 win over Derby on Tuesday evening.
Tamas Priskin nearly gave Derby the perfect start after barely 35 seconds when he found himself unmarked on the edge of the area, but his effort drifted just wide of the post.
Derby continued to push as the first half wore on but could not break down a stubborn Brighton defence with Priskin looking the most likely for the home side.
Derby struggled to influence the second period as Brighton stood firm and Mackail-Smith almost made it two after 79 minutes when he was found by Craig Noone, but his header struck the post.
Next up for the two sides, Brighton host Nottingham Forest on Saturday, while Derby face Crystal Palace on Friday evening.